Inhibiting polymerization of vinyl compounds



Patented June 25, 1946 INHIBITING POLYMERIZATION OF VINYL COMPOUNDS JohnB. Dnrland, Nltro, W. Va., asslgnor to Moncanto Chemical Company, St.Louis, Mo., a corporation of Delaware No Drawing. Application March 2,1944. Serial No. 524,809

18 Claims. 1

The present invention relates to the stabilization of vinyl compoundsand to the tabilized compositions so produced.

It is well known that vinyl compounds as for example vinyl esters, andvinyl aromatic compounds such as styrene, its homologues and analogues,tend to polymerize on standing. In the manufacture of vinyl polymerspremature polymerization even to a very slight extent may render themonomer unfit for use since it may seriously affect the properties ofthe finally polymerized product. For this and other reasons it isessential to prevent premature polymerization and for this purpose it iscommon practice to add an inhibiting agent to the liquid monomer. Anobject of this invention is to provide a new and improved class ofinhibiting agents.

A further object of the invention is to provide a class of cheapmaterials which are effective inhibiting agents. A still further objectis to provide a class of inhibiting agents which are easily removablefrom the liquid monomer after which the polymerization reaction can becarried out in a normal manner. Other and further objects will beapparent from the description following.

In accordance with this invention it has been found that N-nitrosoamines and p-nitroso diaryl amines effectively inhibit thepolymerization of vinyl compounds during storage, shipment anddistillation. While certain amines are known to inhibit thepolymerization of vinyl compounds, the nitroso amines of this group aremore effective than the parent amines from which they are derived. Ofthe N-nitroso amines those having a nitroso group linked to a nitrogenatom which is in turn linked to at least one aryl group are the mosteffective and are therefore preferred.

Typical examples of nitroso amines which can be used in the practice ofthis invention comprise the following: N-nitroso benzyl aniline;N-nitroso dihydro trimethyl quinoline; N-nltroso dihydro trimethylquinoline polymer; N-nitroso di-pnaphthylamine; N-nitroso diphenylamine;p-nitroso diphenylamine; N-nitroso phenothiazine; N-nitroso-S-phenyldihydro trimethyl quinoline and N-nitroso Dhenyl-p-naphthylamine. All ofthe foregoing compounds have been found to possess marked inhibitingaction when incorporated into monomeric styrene. It is to be understoodthat the above are merely illustrative of the invention and otherN-nitroso amines and p-nitroso diaryl amines can be used whereconvenient or desirable.

The new inhibitors are eflective at elevated temperatures as for example100 C.-200 C. as

well as at storage temperatures and eflectively prevent polymerizationduring distillation. They are easily removed during distillation of thevinyl compound and in nowise affect the polymerization of the distilledproducts. The amount of inhibitor to be used will of course varyaccording to the particular composition and conditions under which it isto be used but in general proportions within the range of 0.001 to 5%are satisfactory. Often the merest traces are suiliclent to preventpolymerization entirely.

Among vinyl monomers which can be preserved by incorporating thereinvone of the preferred class of inhibitors are vinyl acetate, divinylbenzene, a methyl styrene, p-methyl styrene, ethyl vinyl benzene, vinylnaphthalene, p-chloro styrene and the like.

As specific examples of the invention which illustrate the' inhibitingpower of the new inhibitors but which are not to be taken as limitativeof the invention; a suitable proportion of inhibitor was charged withparts by weight of freshly distilled styrene into screw cap bottles ofsuitable capacity having the caps lined with tin foil. The samples werethen immersed in a boiling water bath for a total of 20 hours. Viscositytests were then made at 25 C. with a 10 ml. analytical pipette measuringthe time of flow from the upper mark to a lower mark just below thebulb. For

monomeric styrene the time of flow was 11.5 seconds. The viscosities inthe table below are expressed as relative values with monomeric styreneas one. As a further measure of the inhibiting action the polystyrenecontent was determined by a distillation.

By way of comparison styrene without an inhibitor was too viscous fortest after heating for the same length of time.

Storage tests were carried out at approximately 25 C. Freshly distilledstyrene was stored in the dark in contact with 25 gauge sheet steel.0.01% of inhibitor was incorporated into the styrene and samples testedperiodically for increase in viscosity. The condition of the styreneshowed no change after many months or storage as shown in the tablebelow:

After ten months of storage the styrene composition containing N-nitrosobenzyl aniline showed no change at all but remained a colorless wateryliquid. The other inhibited compositions showed slight yellowing. Thecolor was readily removed by distillation. In this connection mentionshould be made of the'fact that if desired, the inhibitors may beemployed in proportions sumcient to stabilize the vinyl compound at roomtemperature, or thereabout, but in proportion insufllcient to stabilizethe composition at elevated temperature and the stabilizing agent leftin the compositions. The compositions can be heated to produe polymericproducts without removal of the stabilizing agent. Exceedingly minutequantities of inhibitor are often sufllcient for this purpose. Forexample, p-nitroso diphenyl amine in 0.01% by weight on the styrene is avery effective inhibitor at 100 C. Smaller amounts are satisfactory forinhibition during storage and permit mass thermal polymerization withoutremoval of the inhibitor.

Again, the invention is not limited to the compositions set forth toillustrate the invention. Other pdlymerizable vinyl compounds can bestabilized with the new inhibitors and other N- nitroso amines andp-nitroso diaryl amines used. The method of adding the inhibitor can bevaried widely. This invention is limited solely by the claims attachedhereto as part of the present specification.

What is claimed is:

1. A liquid composition comprising a vinyl compound and a proportion ofa member of a group consisting of N-nitroso amines and p-nitroso diarylamines suflicient to inhibit polymerization.

2. A liquid composition comprising a vinyl aromatic compound and aproportion of a member of a group consisting of N-nitroso amines andp-nitroso diaryl amines sufllcient to inhibit polymerization.

3. A liquid composition comprising a. styrene and a proportion of amember of a group consisting of N-nitroso amines and p-nitroso diarylamines suflicient to inhibit polymerization.

4. A liquid composition comprising a styrene and a proportion of an'N-nitroso amine suflicient to inhibit polymerization.

5. A liquid composition comprising a styrene and a proportion of anN-nitroso amine having at least one aromatic group linked to the aminonitrogen atom in proportion suiiicient to inhibit polymerization.

6. A liquid composition comprising a styrene and a proportion of anN-nitroso heterocyciic amine sufllcient to inhibit polymerization.

7. A liquid composition comprising styreneand a proportion'oiN-nitrosodihydro trimethyl quinoline suflicient to inhibitpolymerization.

8. A liquid composition comprising styrene and a proportion of N-nitrosobenzyl aniline sumcient tov inhibit polymerization.

9. A liquid composition comprising styrene and a proportion of p-nitr0sodiphenyl amine sumcient to inhibit polymerization.

10. The method or preventing polymerization of a liquid compositioncomprising a vinyl compound which comprises incorporating therein aproportion oi! a member of a group consisting oi N-nitroso amines andp-nitroso diaryl amines sufllcient to inhibit polymerization.

11. The method of preventing polymerization of a liquid compositioncomprising a vinyl aromatic compound which comprises incorporatingtherein a proportion 01 a member or a group consisting of N-nitrosoamines and p-nitroso diary] amines sufllcient to inhibit polymerization.

12. The method of preventing polymerization of a liquid compositioncomprising a styrene which comprises incorporating therein a proportionof a member of a group consisting of N-nitroso amines and p-nitrosodiary] amines sumcient to inhibit polymerization.

13. The method of preventing polymerization of a liquid compositioncomprising a styrene which comprises incorporating therein a proportionoi an N-nitroso amine sufllcient to inhibit polymerizatlon.

14. The method or preventing polymerization of a liquid compositioncomprising a styrene which comprises incorporating therein a proportionof an N-nitroso amine having at least one aromatic group linked to theamino nitrogen atom in proportion suflicient to inhibit polymerization,

15. The method of preventing polymerization of a liquid compositioncomprising a styrene which comprises incorporating therein a proportionof an N-nitroso heterocyclic amine sufllcient to inhibit polymerization.

16. The method or preventing polymerization of a liquid compositioncomprising styrene which comprises incorporating therein a proportion ofN-nitroso dihydro trimethyl quinoline sufllcient to inhibitpolymerization.

17. The method of preventing polymerization of a liquid compositioncomprising styrene which comprises incorporating therein a proportion ofN-nitroso benzyl aniline suillcient to inhibit polymerization.

18. The method of preventing polymerization of a liquid compositioncomprising styrene which comprises incorporating therein a proportion ofp-nitroso diphenyl amine sufllcient to inhibit polymerization.

JOHN R. DURLAND.

